It has been conventional to provide household blenders with an operator's panel with switches whereby a user may select one of a plurality, usually 14, drive motor speeds and further select a mode of energization of the motor. Swanke et al. U.S. Pat. No. 3,678,288 discloses such a blender having 7 speed selection push buttons. The push-buttons drive slider elements which close switches so as to selectively energize various combinations of fields in a drive motor having multiple fields. Field selection provides seven speeds in a high range. Seven speeds in a low range are obtained by applying only half cycles of the AC energizing voltage to the motor when certain combinations of the switches are actuated. Once a speed selection push button is depressed, the motor is energized until an OFF switch is actuated. The device also has a jogger or pulse mode pushbutton which energizes the motor at one speed only as long as the pushbutton is depressed. Pulsing the motor on/off or at high and then low speeds permits the material being processed to fall back to the region of the cutting knives thereby improving the processing of the material.
Ernster et al. U.S. Pat. No. 3,951,351 discloses a blender having a rotary switch for selecting a high or low range of speeds and 5 pushbutton switches for selecting a speed within the selected range. The pushbutton switches connect various segments of the motor field winding in the energizing circuit. This device also includes a pulse mode pushbutton which causes energization of the motor only as long as the pushbutton is depressed. The motor may be energized in the pulse mode at any selected speed.
In Cockroft U.S. Pat. No. 3,548,280 a blender is provided with 10 speed selection switches. An SCR is connected in series with the motor and has a control electrode connected to resistances which are brought into the electrode circuit by actuation of the speed selection switches to control the angle of firing of the SCR and thus the speed of the motor. This device also has a mode selection switch for selecting the manual mode or a cycling or pulse mode in which the motor is alternately energized and deenergized over a plurality of cycles, the number of cycles being set by a potentiometer controlled by a rotatable knob. In a preferred embodiment the on and off intervals are set during manufacture but the patentee suggests that two potentiometers may be provided to enable an operator to vary the on and off times.
Oota et al. U.S. Pat. No. 4,459,524 discloses a food processor having a microcomputer for controlling the firing of a bi-directional thyristor which is connected in series with the drive motor. Manual switches are provided for setting the interval of energization of the motor. However, this device operates at a single motor speed and lacks a pulse mode control
Stottmann U.S. Pat. No. 4,822,172 discloses a microprocessor-based food mixer having UP and DOWN switches for selecting one of 10 drive motor speeds. The switches control the increase/decrease of motor speed during the intervals they are pressed. The device may be operated in a normal mode in which, once a speed is selected, the motor is energized until a stop switch is actuated or the mode is changed. The device may also operate in a timed mode in which the motor is energized for an interval of time, the interval being set by successive actuations of a mix timer switch.
The prior art devices have several disadvantages in that they require motors having special field windings or field winding taps, mechanical push-button switch mechanisms which wear, or which require a long time, relatively speaking, to select the motor speed. None of the devices provide continuous, manual pulse and autopulse modes of operation, nor do they provide an autopulse mode of operation wherein both on/off times and speed modification during on time may be selected by the operator.